Eruption reconstruction, formation of flow-lobe tumuli and eruption duration in the 5900 BP Helgafell lava field (Heimaey), south Iceland

Evolution of the Tibetan Plateau is important for understanding continental tectonics because of its exceptional elevation (~5 km above sea level) and crustal thickness (~70 km). Patterns of long-term landscape evolution can constrain tectonic processes, but have been hard to quantify, in contrast to established datasets for strain, exhumation and paleo-elevation. This study analyses the relief of the bases and tops of 17 Cenozoic lava fields on the central and northern Tibetan Plateau. Analyzed fields have typical lateral dimensions of 10s of km, and so have an appropriate scale for interpreting tectonic geomorphology. Fourteen of the fields have not been deformed since eruption. One field is cut by normal faults; two others are gently folded with limb dips <6o. Relief of the bases and tops of the fields is comparable to modern, internally-drained, parts of the plateau, and distinctly lower than externally-drained regions. The lavas preserve a record of underlying low relief bedrock landscapes at the time they were erupted, which have undergone little change since. There is an overlap in each area between younger published low-temperature thermochronology ages and the oldest eruption in each area, here interpreted as the transition between the end of significant (>3 km) exhumation and plateau landscape development. This diachronous process took place between ~32.5o - ~36.5o N between ~40 and ~10 Ma, advancing northwards at a long-term rate of ~15 km/Myr. Results are consistent with incremental northwards growth of the plateau, rather than a stepwise evolution or synchronous uplift.

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Thermodynamic model of chemical re-magnetization on the example of Girvas paleovolcano of the Onega structure of Karelian craton

Moscow University Bulletin. Series 4. Geology ◽

10.33623/0579-9406-2019-1-38-45 ◽

2019 ◽

pp. 38-45

Author(s):

A. Yu. Bychkov ◽

Yu. A. Popova ◽

O. E. Kikvadze ◽

N. V. Lubnina

Keyword(s):

Thermodynamic Modeling ◽

Thermodynamic Model ◽

Temporal Correlation ◽

Geological Structure ◽

Lava Field ◽

Volcanic Zone ◽

Karelian Craton ◽

Magmatic Gases

Volcano Girvas is a complexly constructed volcano complex of the Yatuli age. Apparently, it is a shield lava volcano, which was probably one of the supply channels of the vast lava field of the western Prionezhie region within the Girvas volcanic zone. Despite the fact that the Girvassky volcano is bare only fragmentary, the structure of the current is perfectly preserved in the rocks, allowing to reconstruct the direction of flow. Among these rocks, there is a zone of postvolcanic hydrothermal changes in the rocks, consisting mainly of nesting and veined tourmalization and silicification, as well as subsequent epidotization, sulfidization, chloritization and albitization. The zones of secondary changes are confined to faults, while their spatial-temporal correlation remains unclear. Reconstruction of the geological structure showed that there were two main processes at the Girvasa volcano: 1) pneumatolysis of type due to magmatic gases separated from gabbro-dolerite sills, 2) heating and circulation of exogenous waters with formation of near propylites. Based on the proposed scheme, thermodynamic modeling was performed.

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Quelques particularites de la partie nord-ouest du volcan cantalien (region des Rhues et de la Sumene)

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.s7-v.2.239 ◽

1963 ◽

Vol S7-V (2) ◽

pp. 239-240

Author(s):

Jean Roux

Keyword(s):

Lava Flow ◽

Basaltic Lava ◽

Lava Field ◽

Basaltic Lava Flow

Abstract The Miocene basalts at the base of Cantal volcano are exposed at approximately uniform heights in the valleys of the area, indicating that there ought to be a branching internal basaltic lava flow with an origin and extent similar to the upper Pliocene basalts of the plateaus. The igneous breccias in the Auzers area exhibit an abnormal thickness of 170 meters. The northwest part of the Moussage lava field, formed of the plateau basalts, is overlain by the Suc du Rond flows indicating that the Suc du Rond basalts, and not those of the plateau, represent the last phase of the Cantal eruption.

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